Method of forming zinc ingots for working



INVENTORS A) $23. g 5

Oct. 7, 1930. T. D. STAY ET AL METHOD OF FORMING ZINC INGOTS FOR WORKING Filed June 4, 1929 llll ITI

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jjjjjj' "flu" 23 7 \6 22 Patented Oct. 7, 1930 UNITED STATES THEBDN n. awa or m wnmnn nonmauxa, or Lnmwoon, omo' PATENT OFFICE mac!) or roams zmc moors ron wonxnm 7 Application fled. June 4, 1929. Serial m; acacia.

The invention relates to the formation of ingots of zinc and zinc base alloys, which ingo'ts are subsequently worked by rolling, forging, extrusion, and thelike.

The production of zines and zinc base al-' loy ingots or cast slabs for working has been attended by numerous disadvantages such as characterize ingots of other metals, and which it is desirable to avoid, as for exam-. 10 ple, piping, which necessitates cropping and corresponding scrap loss. Also, it is pecujliarly characteristic of commercial and 'many zinc basealloys that'they solidify in U the form of large irregular grains, and ingots produced according to prior vcasting practice are difiicult' to work because ofthe tendency of the coarse grain structure 'to cause surface and corner cracking. Another serious difliculty' arises from the development of blisters and pin holes, in sheet rolledfrom zinc slabs or ingots, these defects being due to porosity in the original casting'from which the sheet was rolled. In addition, substantially all commercial'zi necontains iron,vand

v most of it contains cadmium, so that commercial zinc, as well as zin'c' base alloys, tend to liquate orshow segregation when cast, the prejudicialeifectof these phenomena upon ingots to be worked being well known. These features being common to both zinc and its alloys, the term zinc is hereinafter usedin the specification and claims to collectively designate both.

he object of our invention is to provide a method of forming zinc ingots'for working, the ingots having such grain structure and such freedom 'from segregation, .liquation, and porosity,'that the worked metal has high and uniform physical characteristics and 49 does not develop blisters, pin holes, and sur-' face and corner cracks whilebeing worked. Our invention is" predicated on our discovery that'its'stated object is attained-by progressively, gradually andrapidly solidifying a body of molten ,zinc in'an ingot mold from its bottom to its top, while applying heat to the unsolidified'fportionk'of the metal about progressively rising plane of solidificamm .a a

In the practiceof our invention applied r acteristics.

to the formation 'of zinc for working,an ingot mold of'suitable form is supphed with molten metal at a temperature'best suited to the formation of the desired grainstructure' i: of the solidified ingot, the metal being poured into the mold in a careful manner so as to preclude any large amount of splashing of the metal and thereby avoid consequent formation of oxide and nitride occlusions and the development'of other prejudicial char- The metal in the mold is then progressively and gradually solidified from the bottom to the to of the mold while heat is preferably applie to the body of themetal above its progressively rising lane of solidification. Such solidification o the metal may be accomplished by gradually loweringthe mold through a burner or series of burners which apply heat to its walls to keep the upper portion ofthe metal molten and at its desired temperature, andjthrough a sprayor sprays of 'water' applied to the .mold below the burners to progressively coolthe metal subsi santially in that portion of the mold lysprays and burners which are individually controlled to cause the metal to progressively solidify in a gradually rising general plane while being maintained molten above such plane. While gas or other fluid fuel burners are preferably used for heating the upper portion of thejmold and fits contained metal,

it will be understood that such heating may be effected electrically or otherwise.

Apparatus which may be and has been used in the practice of the invention in the several ways just explained is illustrated in the accompanying drawings, of which Fig. 1 a vertical central sectional view of a mold a water sprayyFig. 2 a similar view of a mold passing downwardly through a heater.

passing downwardly through a heater and i lar view of'a stationary mold surrounded by alternately arranged burners and sprays.

The apparatus shown in Fig. 1 comprises a vertically disposed shaft 1 of refractory material suitably supported by posts 2 and provided at its bottom with a gas or other.

fluid fuel burner 3 preferably extending on all sides of the shaft. Below burner 3 there is a spray pipe 4 which also preferably extends on all sides of the shaft, or in other words, completely surrounds the mold. In the course of being lowered through the superposed heater and cooler, there is an ingot mold here shown as consisting of a tubular side Wall member 5 which is preferably square in cross section, and a removable bottom 6 attached to the side wall member by straps 7, the lower edge of the wall being suitably luted in a groove formed in the upper face of the bottom 6. The top of the mold is provided with lugs 8 engaged by hooks 9 attached to a cable 10 which is paid out at a predetermined rate by means of any of the various well known mechanisms for doing this. As the mold is lowered through cooling spray 4., the metal in the mold solidifies in a general plane lying substantially in that of the spray, and the metal above this plane of solidification is maintained in its molten condition by heat from burner 3, the flames of which rise between the wall of the mold and shaft 1.

The apparatus shown in Fig. 2 is similar to that of Fig. 1,the water spray 4 of Fig. 1 being displaced by a vessel 15 provided with a body of water, which if desired may be circulated and kept at a definite horizontal level b means of inlet and outlet pipes 16 and 17. The mold 18, shown in Fig. 2 as bein lowered through the heater and into the cooler, is of the closed bottom integral type, andv may be suspended and lowered in the same manner as explained with reference to Fig. 1.

In the apparatus shown in Fig. 3, a mold 20 of the same form as that shown in Fig. 1 is indicated as resting upon a base 22, and

as being surrounded by a series of water spray pipes 23, 23, 23 and 23. each connected to.

water supply line 24 from which flow of water to each of the several spray pipes-is independently controlled by valves 25, 25, 25 and 25. Between adjacent water spray pipes there are burners 26, 26 and 26", each connected to a fuel supply pipe 27 from which flow of fuel is independently controlled by valves 28, 28 and 28".

In the operation of the apparatus of Fig. 3, valve 25 is first opened to cause water to spray from pipe 23 upon the lower portion of the mold, and burner 26 is lighted to maintain molten the metal in the upper portion of the mold. At the beginning of the cooling operation sprays 23, 23 and 23 are not used, but where necessary the upper burners 26 and 26 may be used, this being determined by a suitable pyrometer placed in the molten metal. As the plane of solidification of the metal rises, burner 26 is turned ofl by closing valve 28, and spray 23 is brought into play by opening valve 25 burner 26 being then lighted if not previously in use. This procedure is followed until the rising plane of solidification reaches the top of the metal in the mold. In the use of this apparatus heat is effectively abstracted from the molten metal through the lower solidified portion of it and through the lower cooled portion of the mold wall, and accordingly in some cases, depending upon the size of the ingot being solidified, it is unnecessary to use the upper sprays and barrier or burners.

A substantial advantage in the use of the spray cooling apparatus of Figs. 1 and 3 is that the ingots may be formed without taper from end toend. When spray cooling is used, open bottom molds having parallel side walls as shown may be employed without liability of water obtaining access to the molds at their bottom joints. By removing the bottoms, the side walls of the molds may be stripped from the solidified ingots, either by a hammer or a press if shrinkage has not been sufiicient to permit the mold to readily strip from the ingot. When the metal is cooled by lowering the molds into the body of water in the manner illustrated in- Fig. 2, it is usually necessary to use closed bottom ingot molds, which, in order to assure the removal of ingots from them, must be tapered outwardly from their bottoms to their tops as illustrated.

From the foregoing description of the construction and operation of, the apparatus g which may be, and which in point of fact has been, used in the practice of our invention and in the attainment of its object, it will be noted that the gradually rising plane of solidification of the metal is not a geometrically true plane, this term being used in the specification and in the claims to describe and define a solidification stratum which is flat as compared to the prior somewhat conical solidification strata incident to the solidification of metal proceeding from the side Walls as Well as the bottom of a mold. The chilling of the mold at and below the "point of application of a cooling medium being rapid, and the mold being maintained at an elevated temperature above the plane of application of the cooling medium, the metal in the moldabove such plane does not chill upon the upper side wall of the mold, and accordingly upwardly and inwardly extending elongate dendrite crystallization of the metal is precluded.

In the practice of each of the several described ways of progressively cooling the metal various advantageous grain structures may be produced. By maintaining that portion of the metal above the rising plane of solidification at a temperature materially surface cracks. It is inherent in both of these procedures that the metal solidifies simultaneously throughout its substantially horizontal rising plane of solidification, as distinguished from solidifying progressively from the Wall of a mold towards the center of the metal in it such simultaneous solidification being due to the continual and uniform extraction of heat by and from the solidifying metal which is beneath the molten metal. Also ingots formed by both of these procedures have substantially uniform compositions throughout.

As a specific example of the practice of our invention in the formation of ingots having fine equiaxed grain structures, we have found that in forming ingots 8 x 8 x 24 inches from zinc of commercial purity, and by the use of the apparatus of Fig. 1, fine equiaxed grain structure, coupled with freedom from porosity and piping are produced by lowering the ingot mold at a rate of about of an inch per minute while spraying on it about 15 to 20 gallons of water per minute, and while maintaining the unsolidified metal at a temperature of about 790 F., the mold having been filled with the metal at an ini tial temperature of about 800 F. In like manner there may be produced ingots of zinc base alloys, which, in' addition to having foregoing characteristics, are substantially free from segregation and liquidation.

The ingots thus produced are substantially free from porosity, piping is decreased or eliminated, and in the case of impure zinc or -zinc base alloys, segregation and liquation are substantially eliminated. The improved grain structure of these ingots is of particular benefit. These characteristics become apparent by comparison of the physical properties of the worked metal with those of metal of the same composition worked from ingots having the coarser grain structures and less desirable ingot characteristics consequent upon the formation of ingots according to the prior practice. Specifically, the tensile strength and elongation of the statutes, we have explained the principle and mode of operation of our invention, and have given specific directions concerning the manner of practicing it. However, we desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described, and with the use of apparatus other than that illustrated.

We claim as our invention:

1. The method of forming in a mold from a molten body of zinc an ingot for working having a readily workable grain structure and of substantially uniform composition throughout, comprising solidifying said body in and simultaneously throughout a substantially horizontal plane-rising gradually and progressively from the bottom to the top of the body of metal, and maintaining in its molten condition the portion of the body of metal above its said rising plane of solidification.

2. The method of forming in a mold from i a molten body of zinc an ingot for working having a fine equiaxed grain structure and of substantially uniform composition throughout, comprising solidifying said body in and simultaneously throughout a substantially horizontal plane rising gradually and progressively from the bottom to the top of the ody of metal, and maintaining at a temperature slightly above its freezing point the portion of the body of metal immediately above its said rising lane of solidification.

3. The method of orming in a mold from a molten body of zinc an ingot for working having a gram structure of elongated form extending parallel to the vertical axis of the ingot as formed and of substantially uniform composition throughout, comprising solidifying said body in and simultaneously throughout a substantially horizontal plane rising gradually and progressively from the bottom our names.

THERON D. STAY. WILLIAM HOLZHAUER.

worked metal are superior, and blisters, pin

holes, surface and corner cracking and other defects due to porosity and poor grain structure are substantially eliminated.

According to the provisions of the patent 

